SUMMARY OF WORK Vascular smooth muscle cells (VSMCs) play a major role in the arterial wall response to injury. VSMCs are normally present in the arterial tunica media where they regulate vascular tone and blood flow. In the vessel wall, VSMCs are surrounded and separated from other cells by extracellular matrix (ECM). Arterial injury leads to proliferation of medical VSMCs and migration of these cells from the media to the intima. These steps are dependent on the local degradation and remodeling of the ECM. Our studies examined the role of adenovirus-mediated wild-type p53 (AdCMV.p53) and tissue inhibitor of metalloproteinase 2 (AdCMV.hTIMP-2) overexpression in vascular smooth muscle cells (VSMCs). In preliminary experiments it was shown that AdCMV.p53 failed to induce VSMC apoptosis in vitro and inhibition of intimal hyperplasia in the rat model of neointima development after carotid injury. In contrast AdCMV.p53 induced melanoma cell apoptosis. Therefore, experiments were aimed at elucidating the role of p21, a p53-effector gene, in the different response of VSMC and melanoma cells to AdCMV.p53. The results showed that the failure of AdCMV.p53 to induce VSMC apoptosis was associated with enhanced p21 expression in these cells. In contrast, in melanoma cells AdCMV.p53 resulted in apoptosis and did not increase p21. In additional experiments it was shown that Ad-mediated p21 overexpression prior to exposure to AdCMV.p53 protected melanoma cells from the apoptosis effect of this viral vector. These findings support the view that p21 plays a fundamental role in the decision fork between programmed cell death and survival and account for the failure of AdCMV.p53 to inhibit neointima development. In a different study it was assessed the effect of AdCMV.hTIMP-2 on VSMC function in vitro and on neointimal development in vivo. Previous studies in the rat model of carotid injury indicated that vascular injury increased activation of matrix metallo-proteinase 2 (MMP2) during the time VSMCs migrated to the intima.TIMP-2 is a physiologic MMP2 inhibitor and AdCMV.hTIMP-2 was previously shown to inhibit MMP2 activity and SMC invasion in cultured VSMC. In this study, 6 month old rats underwent balloon injury of the common carotid artery. The vessel wall was infected either with AdCMV.hTIMP-2 or with the control vector AdCMV.null at the time of balloon injury. AdCMV.hTIMP-2 transgene expression in VSMCs, in vivo, was shown by immunohistochemistry 5 days after injury and infection. At 4 days post-injury and infection, intimal cell number was decreased 36% in AdCMV.hTIMP-2 vs AdCMV.null infected carotid arteries (p<0.05). At 8 days after injury and infection, AdCMV.hTIMP-2 induced a 50% reduction of neointimal growth vs AdCMV.null (p<0.01). In contrast to the changes seen in the neointima, no difference was seen in the area of medial wall. Thus Ad-mediated TIMP-2 overexpression in the rat model of carotid artery injury inhibits SMC migration and decreases the severity of neointimal formation.